Yes. Medical exemptions are a real thing, for real quantifiable reasons.

Religious exemptions are kind of fuzzy, are not an absolute right and can be overridden by circumstance... ie it can be determined that you have a sincere religious issue with vaccination (or whatever else you don't like) but if you're an ER trauma surgeon/nurse you might have to get the vaccine anyway. Just like the flu shot, since both flu and covid are dangerous to many hospital patients and pretty much all ICU patients.

Another example... sabbath days. Don't know of any (US) airlines which guarantee sabbath days off, which would obviously be in gross violation of seniority. Never heard of it in any other 24/7 seniority-based shift work industry either. So union seniority pretty clear trumps sincere religious beliefs (as it should).